Bismuth-containing laser markable compositions and methods of making and using same

ABSTRACT

The present invention relates to additive, pigment or colorant materials which may be used for laser marking. The materials comprise oxides of bismuth and at least one additional metal. Preferred laser-markable bismuth-containing oxide compounds are of the formula Bi x M y O z , where M is at least one metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr, Ca, Mg, Mo, W, Sb, Cr, Ba and Ce, x is from about 0.3 to about 70, y is from about 0.05 to about 8, and z is from about 1 to about 100. The bismuth-containing material may be dispersed in a substrate which is subsequently irradiated by a laser to provide a contrasting mark in the irradiated region.

FIELD OF THE INVENTION

[0001] The present invention relates to addition, pigment or colorantmaterials which may be used for laser marking, and more particularlyrelates to bismuth-containing laser markable compositions, and methodsof making and using such compositions.

BACKGROUND INFORMATION

[0002] The use of titanium dioxide as a laser markable pigment isdisclosed in U.S. Pat. No. 5,091,284. However, laser marks produced fromtitanium dioxide suffer from poor contrast and durability. Although manydifferent types of pigments are known, a need exists for a pigment whichcan be added to a substrate to produce high contrast durable lasermarks.

SUMMARY OF THE INVENTION

[0003] This invention relates to the use of bismuth-containing compoundsas an additive, pigment or colorant. The bismuth containing compoundsare useful in substrates comprising organic chemical compositions suchas plastics, rubbers and the like, and coating compositions such aspaints, printing inks and the like. The bismuth-containing compounds arealso useful in inorganic chemical composition substrates such as glassenamels, porcelain enamels and the like. The present bismuth-containingcompounds may be used in such compositions to impart unique propertiessuch as the ability to make high contrast laser marks and/or colorchanging interactions with laser beams, unique electronic properties andhigh IR reflectance.

[0004] An aspect of the present invention is to provide a pigment of theformula Bi_(x)M_(y)O_(z), where M is at least one metal selected fromZn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr, Ca, Mg, Mo, W,Sb, Cr, Ba and Ce, x is from about 0.3 to about 70, y is from about 0.05to about 8, and z is from about 1 to about 100.

[0005] A further aspect of the present invention is to provide a lasermarkable compound comprising an oxide of bismuth and at least oneadditional metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y,Nb, La, Ta, Pr, Ca, Mg, Mo, W, Sb, Cr, and Ce.

[0006] Another aspect of the present invention is to provide a lasermarkable substrate comprising a substrate material and abismuth-containing compound dispersed in the substrate material.

[0007] A further aspect of the present invention is to provide lasermarked substrate comprising a substrate material, a bismuth-containingcompound dispersed in the substrate material, and a laser-marked portionof the bismuth-containing compound providing a contrasting mark on thesubstrate material.

[0008] Another aspect of the present invention is to provide a method ofmaking a laser markable compound comprising the steps of mixing bismuthoxide or precursors thereof with at least one additional metal oxide orprecursors thereof, and heating the mixture.

[0009] A further aspect of the present invention is to provide a methodof making a laser markable substrate comprising dispersing abismuth-containing compound in a substrate material.

[0010] Another aspect of the present invention is to provide a method oflaser marking an article comprising providing a substrate including abismuth-containing compound and irradiating at least a portion of thesubstrate with a laser to form a marking thereon.

[0011] These and other aspects of the present invention will be moreapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIGS. 1a and 1 b are partially schematic isometric sectional viewsillustrating a process of laser marking a substrate which includes abismuth-containing composition in accordance with an embodiment of theinvention.

[0013] FIGS. 2-11 are graphs of reflectance versus wavelength forsubstrates comprising various bismuth-containing laser markablecompositions of the invention.

[0014] FIGS. 12-14 are graphs of reflectance versus wavelength forcomparative substrates.

DETAILED DESCRIPTION

[0015]FIGS. 1a and 1 b schematically illustrate a laser markingoperation in accordance with an embodiment of the invention. A substrate10 includes particles 12 of the present bismuth-containing compoundsdispersed therein. As illustrated in FIG. 1b, a portion 14 of thesubstrate 10 that has been irradiated with a laser beam (not shown)appears as a marking which contrasts with the unmarked portion of thesubstrate. The contrasting marked portion has different visualcharacteristics in comparison with the rest of the substrate, e.g., adifferent lightness value and/or a different color value. This contrastresults from the interaction of the laser beam with thebismuth-containing compound particles. While not intending to be boundby theory, upon irradiation, the particles of the laser markingcompounds may interact with the laser energy by scattering, reflectingor absorbing the energy, and a chemical reaction may occur with thesubstrate material, e.g., paint or plastic material matrix. Thereactions may occur under reducing conditions such that thebismuth-containing compounds change to a state of reduced oxygencontent.

[0016] As used herein, the term “laser markable compound” means acompound that can be dispersed in a substrate and provide a contrastingmark on the substrate after the region has been irradiated by a laser.The resultant marked region contrasts with the non-irradiated region,e.g., the marking may have a different lightness value and/or colorvalue compared with the non-irradiated region. For example, the lasermarkable compounds preferably provide contrasting marks having differentlightness values ΔL as determined by the standard CIELAB scale. Thedifference in lightness values ΔL between the marked and unmarkedregions typically has an absolute value of greater than about 10.Preferably, the absolute value of ΔL is greater than about 20, morepreferably greater than about 25. In a particularly preferredembodiment, the absolute value of ΔL is about 30 or higher.

[0017] The term “substrate” as used herein means any material in whichthe present bismuth-containing compounds may be incorporated, includingcoatings and bulk materials in various forms. The bismuth-containingcompounds may be dispersed homogeneously or non-homogeneously in thesubstrate.

[0018] The present laser markable compounds comprise Bi and at least oneadditional metal. Preferably, the compounds are oxides of Bi and theadditional metal(s), but may alternatively comprise oxide-freecompounds, hydrates, carbonates, sulfates, sulfides or other compoundscontaining the bismuth and additional metal(s). The additional metalsare preferably Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr,Ca, Mg., Mo, W, Sb, Cr, Ba and Ce.

[0019] Preferred laser markable bismuth-containing oxide compounds ofthe present invention are of the formula Bi_(x)M_(y)O_(z), where M is atleast one metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y,Nb, La, Ta, Pr, Ca, Mg, Mo, W, Sb, Cr, Ba and Ce. Particularly preferredmetals include Zn, Si, Zr, Al and Sn. In this formula, x is from about0.3 to about 70, y is from about 0.05 to about 8, and z is from about 1to about 100. More preferably, x is from about 2 to about 64, y is fromabout 0.3 to about 4, and z is from about 2 to about 98. For lasermarking contrast, it has been found that higher bismuth content tends toresult in higher contrast of the mark. Preferred ratios of x/y aregreater than 2 or 3. More preferred ratios of x/y are greater than about5 or 10, more preferably greater than about 20. The bismuth-containingcompounds are typically provided in particulate form having averageparticle sizes from about 0.5 to about 40 micron, preferably from about0.8 to about 4 micron.

[0020] The bismuth-containing compounds are provided in the substrate insufficient amounts to provide laser marks of sufficient contrast.Furthermore, the compounds may be provided in sufficient amounts forcoloring purposes. The bismuth-containing compounds preferably comprisefrom about 0.1 to about 70 weight percent of the substrate, morepreferably from about 2 to about 50 weight percent.

[0021] In accordance with an embodiment of the present invention, thelaser markable compounds are selected such that they exhibitsufficiently high contrast laser marking qualities. The presentcompounds are preferably formed by high temperature reaction of bismuthoxide and other metal oxide(s). The unique compounds are then used as apigment type material in the substrate, e.g., paints and plastics. Byaddition of these pre-reacted unique chemical structures to thesubstrate compositions, the laser marking contrast properties aregreatly enhanced. In preferred embodiments, the heat build-up is alsogreatly reduced due to unique IR reflecting properties, and electronicproperties may be improved.

[0022] The bismuth-containing laser markable compounds may be made bymixing Bi metal oxides and additional metal oxides or precursorsthereof, such as nitrates, carbonates, sulfates, etc, and heating themixture and grinding the materials. Other methods of making the lasermarkable compounds include wet chemical precipitation reactions, sol gelreaction, and vapor phase reactions to make the compounds or coatings onthe surfaces of the compounds.

[0023] Various methods may be used to disperse the bismuth-containinglaser markable compound into the substrate. For example, paints may bemade by conventional mixing operations using cowles, horizontal mills,bead mills, shakers, attritors and the like. The bismuth-containingcompounds may be mixed into plastic and other substrates usingconventional extruders, molding equipment, brabenders and the like.

[0024] Uses of the present bismuth-containing laser markable compoundsinclude many applications such as plastic and paint applications for theautomotive, architectural and electronics industries, and otherindustrial and military applications. One of the unique properties ofcoatings which include the present bismuth-based materials is theability to produce high contrast marks upon irradiation by a laser beam.Use of the present compounds in combination with, e.g., paint andplastic chemistries allows for extremely high contrast marks to beformed by the laser. These marks can be used for decorative oridentification purposes.

[0025] Plastic or rubber substrate compositions that can be colored andmarked according to this invention are based upon polymeric materialsthat can be natural or synthetic. Examples include natural resins,rubber, chlororubber, casein, oil-modified alkyd resins, viscose,cellulose acetate, cellulose propionate, cellulose acetobutyrate,nitrocellulose, or other cellulose ethers or esters. Synthetic organicpolymers produced by polymerization, polyaddition, or polycondensationin thermosetting or thermoplastics can also be colored by thisinvention. Examples are polyethylene, polystyrene, polypropylene,polyisobutylene, polyvinylchloride, polyvinylacetate, polyacrylonitrile,poly acrylic acid, other polyolefins and substituted polyolefins, aswell as methyacrylic acid esters, butadiene, as well as co polymers ofthe above mentioned. Examples from polyaddition and polycondensationresins are the condensation products of formaldehyde with phenols,phenolic resins, urea, thiourea, and melamine, amino resins, polyesters,polyamides, polycarbonates, and/or silicones. These polymers can bepresent individually or as mixtures as plastic material or melts spuninto fibers. They can also be dissolved as film formers or binders forlaquers, paints, or printing inks such as linseed oil, nitrocellulose,melamine resins, acrylic resins, ureaformaldehyde resins and the like.The pigmentary use of the present bismuth-containing compounds in othercoatings or materials such as carbon-carbon composites may also provideadvantages with regard to IR reflection. Also a plastic body as asubstrate which would contain the pigment (such as vinyl siding) and/orany substrate (glass, ceramic, metal, plastic, composite) having thereonan organic coating or paint which would contain and utilize the highcontrast laser markability, electronic properties, or low heat build-upproperties of the bismuth containing pigments.

[0026] Another use of the present bismuth-containing compounds is inglass-ceramic enamels for applications such as colored borders aroundglass sheets used for automobiles to enhance appearance and to preventUV degradation of underlying adhesives. Architectural, container andother glass or ceramic decorative applications where the compounds arestable and can impart desirable property improvements are also possiblein accordance with the present invention.

[0027] Glass-ceramic enamel compositions may comprise from 1 to 70 wt %of the bismuth-containing compounds, such as ZnBi₃₈O₆₀, and from 30 to99 wt % solid glass frit compositions, or a combination of two or morefrits. Additional oxide pigments may be added to the enamel compositionssuch as CuCr₂O₄,(CO,Fe)(Fe,Cr)₂O₄ and the like. Printable enamel pastemay be made from 60 to 85 wt % of above solids power, plus 15 to 40 wt %of a suitable carrying vehicle or medium which can be, e.g., screenprinted, roll coated or sprayed. Such glass-ceramic enamels may beapplied to automotive glass substrates, architectural glass substrates,container glass substrates, and/or metal substrates.

[0028] The following examples are intended to illustrate various aspectsof the invention, and are not intended to limit the scope of theinvention.

Bismuth Titanate Compounds

[0029] A sample designated 267-010a was made from 59.3 g Bi₂O₃ and 40.7g TiO₂. The powders were mixed together and heated at 2,110° F. foreight hours. The sample was ground into a fine powder which had an offwhite or pastel yellow color. X-ray diffraction identified Bi₂Ti₄O₁₁ asthe main crystalline phase.

[0030] A sample designated 267-011a was made from 79.5 g Bi₂O₃ and 20.5g TiO₂. The powders were mixed together and heated at 2,110° F. foreight hours. The sample was ground into a fine powder which had an offwhite color. X-ray diffraction identified Bi₄Ti₃O₁₂ as the maincrystalline phase.

[0031] A sample designated 267-012b was made from 98.31 g Bi₂O₃ and 1.69g TiO₂. The powders were mixed together and melted at 1832° F. for tenminutes, and then poured into water. The sample was ground into a finepowder which had an off white color. X-ray diffraction identifiedBi₁₂TiO₂₀ as the main crystalline phase.

[0032] A sample designated 267-013a was made from 97.2 g Bi₂O₃ and 2.8 gTiO₂. The powders were mixed together and melted in a crucible at 1,832°F. for ten minutes and then poured into a water bath. The sample wasground into a fine powder which had a pastel yellow color. X-raydiffraction identified Bi₁₂TiO₂₀ as the main crystalline phase.

[0033] Additional bismuth titanate compounds for high contrast lasermarking may include Bi₈TiO₁₄, Bi₂Ti₂O₇, Bi₂₀TiO₃₂ and other crystalline,partially crystalline and amorphous compounds.

Bismuth Ferrite Compounds

[0034] A sample designated 267-016b was made from 97.2 g Bi₂O₃ and 2.8 gFe₂O₃. The powders were mixed together and melted in a crucible at1,652° F. for 10 minutes, 1,832° F. for ten minutes, and then pouredinto a water bath. The sample was ground into a fine powder which had ayellow-orange color. X-ray diffraction identified only an amorphousphase present.

[0035] Additional bismuth ferrite compounds for high contrast lasermarking may include Bi₂Fe₄O₉, BiFeO₃, Bi_(3.43)Fe_(0.57)O₆, Bi₂₄Fe₂O₃₉,Bi₂₅FeO₄₀, Bi₄₆Fe₂O₇₂, Bi₃₆Fe₂O₅₇ and other crystalline, partiallycrystalline and amorphous compounds.

Bismuth Aluminate Compounds

[0036] A sample designated 267-022a was made from 99.1 g Bi₂O₃ and 0.9 gAl₂O₃. The powders were mixed together and melted in a crucible at1,832° F. for ten minutes, and then poured into a water bath. The samplewas ground into a fine powder which had a light yellow color. X-raydiffraction identified Bi₂O₃ and Bi₂₄Al₂O₃₉ phases present.

[0037] Additional bismuth aluminate compounds for high contrast lasermarking may include AlBiO₃, Al₄Bi₂O₉, Bi₄₈Al₂O₇₅ and other crystalline,partially crystalline and amorphous compounds.

Bismuth Zirconate Compounds

[0038] A sample designated 267-024a was made from 95.7 g Bi₂O₃ and 4.3 gZrO₂. The powders were mixed together and melted in a crucible at 1,832°F. for ten minutes, and then poured into a water bath. The sample wasground into a fine powder which had a yellow-orange color. X-raydiffraction identified Bi₂O₃, ZrO₂ and Bi₂₄Al₂O₃₉ phases present.

[0039] A sample designated 267-024b was made from 54.0 g Bi₂O₃ and 46.0g ZrO₂. The powders were mixed together and heated on a mullite plate at1,652° F. for seven hours. The sample was ground into a fine powderwhich had a yellow-orange-tan color. X-ray diffraction identified Bi₂O₃,ZrO₂, Bi₁₂SiO₂₀ and SiO₂ phases present. Based on stochiometry, theexpected phase is Bi₂Zr₃O₉. However, this phase is not in the xrdcomputer database.

[0040] A sample designated 267-024c was made from 71.6 g Bi₂O₃ and 28.4g ZrO₂. The powders were mixed together and heated on a mullite plate at1,652° F. for seven hours. The sample was ground into a fine powderwhich had a yellow-orange color. X-ray diffraction identified Bi₂O₃,ZrO₂ and Bi₁₂SiO₂₀ phases present. Based on stochiometry, the expectedphase is Bi₄Zr₃O₁₂. However, this phase is not in the xrd computerdatabase.

[0041] Other bismuth zirconate crystalline, partially crystalline andamorphous compounds could be included for high contrast laser markingapplications.

Bismuth Phosphate Compounds

[0042] Bismuth phosphate compounds for high contrast laser marking mayinclude BiP₅O₁₄, Bi(PO₃)₃, BiPO₄, Bi₂P₄O₁₃, Bi₄P₂O₁₁, Bi₃PO₇, Bi₅PO₁₀,Bi₁₂P₂O₂₃, Bi₂₃P₄O_(44.5), Bi_(3.69)P_(0.31)O_(6.31),Bi_(7.68)P_(0.32)O_(12.32) and other crystalline, partially crystalline,and amorphous compounds.

Bismuth Stannate Compounds

[0043] A sample designated 267-036a was made from 50.8 g Bi₂O₃ and 49.2g SnO₂. The powders were ground together in water for 1.5 hour to mixthoroughly, and then dried at 220° F. Powders were heated together at1,958° F. for seven hours. The sample was ground into a fine powderwhich had a tannish off-white color. X-ray diffraction identifiedBi₂Sn₂O₇ and SnO₂ phases present.

[0044] A sample designated 267-038a was made from 99.0 g Bi₂O₃ and 1.0 gSnO₂. The powders were mixed together and melted in a crucible at 1,832°F. for twenty minutes, and then poured into a water bath. The sample wasground into a fine powder which had an orange-yellow color. X-raydiffraction identified Bi₁₂SiO₂₀ and SiO₂ phases present.

[0045] Additional bismuth stannate compounds for high contrast lasermarking may also include Bi₂Sn₃O₉, Bi₁₂SnO₂₀,Bi_(3.94)Sn_(0.06)O_(6.02), Bi₆₄SnO₉₈, Bi₇Sn_(0.1)O_(10.7) and othercrystalline, partially crystalline and amorphous compounds.

Strontium Bismuth Oxide Compounds

[0046] A sample designated 267-047a was made from 87.1 g Bi₂O₃ and 12.9g SrCO₃. The powders were mixed together and melted in a crucible at1,832° F. for ten minutes, 2,000° F. for ten minutes, 2,100° F. for oneminute, and then poured into a water bath. The sample was ground into afine powder which had an yellow color. X-ray diffraction identifiedcrystalline Bi₂O₃ and SrSiO₃ phases present, and an amorphous phasepresent.

[0047] Additional strontium bismuth oxide compounds for high contrastlaser marking may include Sr₆Bi₂O₉, Sr₃Bi₂O₆, Sr₂Bi₂O₅, Sr₃BiO_(5.4),Sr₃BiO₂, Sr_(1.5)Bi_(0.5)O_(2.75), Sr_(1.2)Bi_(0.8)O₃,Sr_(0.9)Bi_(1.1)O_(2.55), Sr₃Bi₄O₉, Sr_(0.74)Bi_(1.26)O_(2.63), SrBi₂O₄,Sr_(2.25)Bi_(6.75)O_(12.38), SrBi₄O₇, Sr_(0.19)Bi_(0.81)O_(1.4),Sr_(0.16)Bi_(3.84)O_(5.92) and other crystalline, partially crystallineand amorphous compounds.

Yittrium Bismuth Oxide Compounds

[0048] A sample designated 267-049a was made from 83.8 g Bi₂O₃ and 16.2g Y₂O₃. The powders were mixed together and melted in a crucible at1,832° F. for ten minutes and then 2,200° F. for ten minutes. The samplewas ground into a fine powder which had an orangish yellow color. X-raydiffraction identified crystalline Y_(0.285)Bi_(0.715)O_(1.5) and Bi₂O₃phases present.

[0049] Additional yittrium bismuth oxide compounds for high contrastlaser marking include BiYO₃, Bi_(1.5)Y_(0.5)O₃,Bi_(0.67)Y_(0.33)O_(1.5), Bi_(1.55)Y_(0.45)O₃, Bi_(1.87)Y_(0.13)O₃,Bi_(1.9)Y_(0.1)O₃, Bi₁₉YO₃₀ and other crystalline, partially crystallineand amorphous compounds.

Bismuth Niobate Compounds

[0050] A sample designated 267-059a was made from 98.8 g Bi₂O₃ and 1.2 gNb₂O₅. The powders were mixed thoroughly together and heated in acrucible at 1,832° F. for ten minutes, 2,000° F. for ten minutes, andthen water quenched. The sample was ground into a fine powder which hada slight orange color. X-ray diffraction identified crystallineBi_(5.6)Si_(0.5)O_(9.4), Bi₂O₃ and/or BiO phases as possibly beingpresent.

[0051] Additional bismuth niobate compounds for high contrast lasermarking may include Bi₃Nb₁₇O₄₇, Bi₂Nb₁₀O₂₈, Bi₈Nb₁₈O₅₇, BiNbO₄,Bi₅Nb₃O₁₅, Bi_(1.70)Nb_(0.30)O_(3.30), Bi₁₂Nb_(0.29)O_(18.7),Bi_(7.84)Nb_(0.16)O_(12.16) and other crystalline, partially crystallineand amorphous compounds.

Bismuth Lanthanum Oxide Compounds

[0052] A sample designated 267-063a was made from 48.8 g Bi₂O₃ and 51.2g La₂O₃. The powders were mixed thoroughly by wet milling together in analumina mill and media and then dried at 220° F. The sample was heatedon a mullite plate at 1,742° F. for twenty four hours and then airquenched. The sample was ground into a fine powder which had a yelloworange color. X-ray diffraction identified crystalline BiLa₂O_(4.5) andBi₈La₁₀O₂₇ phases as being present.

[0053] Additional bismuth lanthanum oxide compounds for high contrastlaser marking may include Bi_(0.92)La_(1.08)O_(3.03),Bi_(0.4)La_(0.6)O_(1.5), BiLa₂O_(4.5) and other crystalline partiallycrystalline and amorphous compounds.

Bismuth Tantalum Oxide Compounds

[0054] A sample designated 267-064a was made from 97.6 g Bi₂O₃ and 2.4 gTa₂O₅. The powders were mixed thoroughly by wet milling together in analumina mill and media and then dried at 220° F. The sample was heatedon a mullite plate at 1,418° F. for twenty-four hours and then airquenched. The sample was ground into a fine powder which had a yelloworange color. X-ray diffraction identified crystallineBi_(7.8)Ta_(0.2)O_(12.20) as a major phase and Bi₂O₃, Bi₂₄Al₂O₃₉ andSiO₂ minor phases as being present.

[0055] Additional bismuth tantalum oxide compounds for high contrastlaser marking may include Bi_(3.0)TaO₇₀, BiTaO₄, BiTa₇O₁₉ and othercrystalline, partially crystalline and amorphous compounds.

Bismuth Praseodymium Oxide Compounds

[0056] A sample designated 267-068a was made from 74.6 g Bi₂O₃ and 25.4g Pr₂O₃. The powders were mixed thoroughly and then heated on a mulliteplate at 1,565° F. for five hours and then quenched in liquid nitrogen.The sample was ground into a fine powder which had a yellow green color.X-ray diffraction identified crystalline Bi_(1.35)Pr_(0.65)O₃ as a majorphase and Bi₂O₃ and SiO₂ minor phases as being present.

[0057] A sample designated 267-068b was made from 94.7 g Bi₂O₃ and 5.3 gPr₂O₃. The powders were mixed thoroughly and then heated on a mulliteplate at 1,490° F. for five hours and then quenched in liquid nitrogen.The sample was ground into a fine powder which had a yellowish tancolor. X-ray diffraction identified crystalline Bi_(1.854)Pr_(0.146)O₃as a major phase and Bi₂O₃ and Bi₁₂SiO₂₀ minor phases as being present.

[0058] A sample designated 267-069a was made from 96.5 g Bi₂O₃ and 3.5 gPr₂O₃. The powders were mixed thoroughly and then heated on a mulliteplate at 1,454° F. for five hours and then quenched in liquid nitrogen.The sample was ground into a fine powder which had a yellowish tancolor. X-ray diffraction identified crystalline Bi_(1.904)Pr_(0.096)O₃as a major phase and Bi₂O₃ and Bi₁₂SiO₂₀ minor phases as being present.

[0059] Additional bismuth praseodymium oxide compounds for high contrastlaser marking may include other crystalline, partially crystalline, andamorphous compounds.

Bismuth Calcium Oxide Compounds

[0060] A sample designated 267-075a was made from 90.3 g Bi₂O₃ and 9.7 gCaCO₃. The powders were mixed thoroughly and the sample was heated on amullite plate at 1,562° F. for seven hours and then air quenched. Thesample was ground into a fine powder which had a yellow orange-browncolor. X-ray diffraction identified Bi₂O₃, Bi₂₄Al₂O₃₉, Ca(OH)₂ andBi_(1.6)Ca_(0.4)O_(2.8) phases as being present.

[0061] Additional bismuth calcium oxide compounds for high contrastlaser marking may include Bi₆Ca₇O₁₆, Bi₂Ca₂O₅,Bi_(1.09)Ca_(0.91)O_(2.55), Bi₁₀Ca₇O₂₂, Bi₆Ca₄O₁₃, Bi₂CaO₄, Bi₁₄Ca₅O₂₆,Bi_(3.11)Ca_(0.89)O_(5.56), Bi_(1.6)Ca_(0.4)O_(2.8) and othercrystalline, partially crystalline and amorphous compounds.

Bismuth Zinc Oxide Compounds

[0062] A sample designated 174-115e was made from 97.7 g Bi₂O₃ and 2.3 gZnO. The powders were mixed thoroughly and the sample was heated in acordierite sagger at 1,380° F. for sixty-five hours. The sample wasground into a fine powder which had an off white color. X-raydiffraction identified the ZnBi₃₈O₆₀ phase as being present.

[0063] Additional bismuth zinc oxide compounds for high contrast lasermarking may include Bi₄₈ZnO₇₃, Bi_(7.65)Zn_(0.35)O_(11.83), BiZn₃₈O₅₈and other crystalline, partially crystalline and amorphous compounds.

Bismuth Silicate Compounds

[0064] A sample designated 174-115c was made from 97.9 g Bi₂O₃ and 2.1 gSiO₂. The powders were mixed thoroughly and the sample was heated in acordierite sagger at 1,530° F. for fourteen hours. The sample was groundinto a fine powder which had an off white color. X-ray diffractionidentified Bi₁₂SiO₂₀, Bi₂O₃ and Bi₂SiO₅ phases as being present.

[0065] Additional bismuth silicate compounds for high contrast lasermarking may include Bi₄Si₃O₁₂ and other crystalline, partiallycrystalline and amorphous compounds.

[0066] In addition to the above-noted compounds, bismuth cupratecompounds for high contrast laser marking may include Bi₂CuO₄ and othercrystalline, partially crystalline and amorphous compounds.

[0067] Alternatively, bismuth magnesium oxide compounds for highcontrast laser marking may include Bi₁₂MgO₁₉, Bi₁₈Mg₈O₃₆ and othercrystalline, partially crystalline and amorphous compounds.

[0068] Bismuth-containing compounds, such as those described in thepreceding examples, may be used in accordance with the present inventionto produce laser marks on or in various types of substrates. A selectedportion of the substrate comprising the bismuth-containing compound isirradiated with a beam to form a permanent marking therein or thereon.For many types of markings, the irradiated portion of the substratesurface may comprise from about 0.1 to about 99 percent of the totalsurface area of the substrate, typically from about 1 to about 95percent. A laser is preferably used to selectively irradiate thesubstrate. However, other forms of focused energy may be used inaccordance with the present invention. Irradiation may be achieved bymoving a laser beam over a stationary substrate using conventional beamsteering methods, by moving the substrate in relation to the laser beamand/or by masking the substrate. Laser irradiation is typically achievedby directing the beam directly against the surface of the substrate tobe marked, but may also be achieved by directing the beam through therear side of a sufficiently transparent substrate.

[0069] Suitable lasers for use in accordance with the present inventioninclude neodymium:yttrium aluminum garnet (Nd:YAG) lasers, carbondioxide (CO₂) lasers, diode lasers, excimer lasers and the like.

[0070] Typical YAG lasers emit light in the near-infrared spectrum atwavelengths of 1064 nm. Such lasers typically have continuous poweroutputs of from about 1 to about 50 watts, and can be operated in apulsed mode at typical peak powers of from about 1 watt to about 45kilowatts. For pulsed mode operation, frequencies of from about 1 toabout 64,000 pulses/second may be used.

[0071] Typical CO₂ lasers emit light in the far-infrared region of thespectrum, with intensity spikes at wavelengths of 9.8 and 10.6 microns.Such CO₂ lasers typically operate at a continuous output power of fromabout 1 to about 40 watts.

[0072] In accordance with the present invention, the size of the laserspot that impinges the substrate is typically greater than 0.1 micron indiameter, preferably from about 40 to about 500 microns, and morepreferably from about 50 to about 125 microns. The speed at which thelaser beam travels across the surface of the substrate preferably rangesfrom 0 to about 100 inches/second (up to about 250 cm/second), morepreferably from about 1 or 2 to about 20 inches/second (about 2.5 or 5to 50 cm/second) for most thicknesses and compositions. The laser beammay be projected with a seam overlap of 0 to 100 percent, preferablyfrom about 10 to about 90 percent for many applications. The laserparameters are controlled in order to provide sufficient localizedheating of the bismuth-containing compound, while avoiding unwanteddamage to the substrate.

[0073] The laser beam, the movement of which can be controlled by acomputer, may be used to create discrete symbols or designs or,alternatively, may be serially indexed across the surface of thesubstrate to create multiple symbols or designs at the same time. Forexample, a word may be created by separately making each letter of theword with the laser, or by rastering the laser across the entire word toform all of the letters at the same time. A single laser beam may beused for marking in accordance with the present invention.Alternatively, two or more laser beams may be used.

[0074] During the irradiation step, the surface of the substrate may beexposed to any desired type of atmosphere. For example, the atmospheremay comprise air at atmospheric, sub-atmospheric or super-atmosphericpressures. Furthermore, the atmosphere may comprise an inert gas such asnitrogen, argon or carbon dioxide, an oxidizing atmosphere such as airor oxygen, a reducing atmosphere such as hydrogen or carbon monoxide, ora vacuum. Oxidizing or reducing gases can be used in a combination withinert gases.

[0075] Laser marking tests were performed using severalbismuth-containing compounds of the present invention. The followingapplication and laser marking procedures were used in laser markingtests.

Epoxy Coating Test

[0076] Waterbased epoxy (Sherwin Williams Hydralon B)—50 g

[0077] Bismuth-containing pigment—10 g

[0078] Defoamer (Byk 023)—0.05 g

[0079] Glass beads—50 g

[0080] Shake for 30 minutes; filter the dispersion; add one parthardener (Sherwin Williams KEM Aqua Hydralon B) to 2 parts of thedispersion; produce a film with the finished paint on an aluminum paneland let air dry overnight; mark the film surface with YAG or CO₂ laserto produce high contrast marks; and measure the contrast between theunmarked and marked surfaces with a spectrophotometer.

Plastic Test

[0081] Thermoplastic polyurethane resin (Bayer 795 U)—195 g

[0082] Bismuth-containing pigment—5 g

[0083] Shake for 2 minutes; injection mold the samples with a standardinjection molding machine at 395° F. into color chips; mark the chipswith YAG or CO₂ laser to produce high contrast marks; and measure thecontrast between the unmarked and marked surfaces with aspectrophotometer.

[0084] For YAG laser marking, the following parameters were used: 10,000pulses/second; 20 inches per second; 32 amps power; 0.005 dot size; and40 percent seam overlap. For CO₂ laser marking, the following parameterswere used: 50 percent of 35 watt power; 36 inches/minute; and 500 dpi.

[0085] Table 1 lists the color values of each epoxy coating samplebefore and after laser marking. The standard CIELAB L*a*b* system wasused to define the color of the samples. The L* value refers to thelightness of the sample, with L*=100 designating the lightness upperlimit and L*=0 designating the darkness lower limit. The a* valuedescribes the red or green value of the pigment, with a positive a*value designating red, and a negative a* value designating green. The b*value represents the blue or yellow value, with a positive b* valuedesignating yellow and a negative b* value designating blue. The ΔL*,Δa* and Δb* values represent the difference in the L*, a* and b* valuesbetween the unmarked and marked samples. The Δ* values are a measure ofthe combined difference in lightness and color values between theunmarked and marked samples. TABLE 1 Epoxy Coating Laser Mark ContrastSample ID L* a* b* ΔL* Δa* Δb* ΔE* White 87.88 −0.36 4.38 267-010A267-010A 62.45 1.51 6.39 −25.43 1.87 2.00 25.58 Marked White 89.99 −0.224.40 267-010A′ 267-010A′ 63.86 1.46 6.22 −26.13 1.67 1.82 26.25 MarkedWhite 87.87 −0.97 7.89 267-011A 267-011A 60.66 1.71 7.45 −27.21 2.68−0.44 27.35 Marked Light 86.24 −5.59 18.96 Yellow 267-12B 267-12B 53.422.07 9.08 −32.82 7.67 −9.87 35.12 Marked Light 88.25 −5.52 23.19 Yellow267-013A 267-013A 54.20 1.86 9.64 −34.05 7.37 −13.56 37.38 Marked Yellow77.48 2.78 46.39 267-016B 267-016B 53.73 2.03 21.98 −23.76 −0.76 −24.4134.07 Marked Yellow 85.76 −7.82 21.46 267-022A 267-022A 58.75 −1.6614.00 −27.01 6.15 −7.46 28.69 Marked Yellow 86.37 −6.44 38.04 267-024A267-024A 47.96 1.57 13.03 −38.41 8.01 −25.01 46.53 Marked Light 87.57−3.30 13.46 Yellow 267-038A 267-038A 57.84 1.36 9.28 −29.72 4.66 −4.1730.38 Marked Light 89.05 −5.66 13.68 Yellow 267-047A 267-047A 53.03 2.076.73 −36.02 7.73 −6.96 37.49 Marked Yellow 84.46 −5.38 36.02 267-049A267-049A 60.62 −1.19 19.56 −23.84 4.19 −16.45 29.27 Marked Light 87.99−8.25 22.84 Yellow 267-059A 267-059A 52.12 0.01 11.73 −35.87 8.26 −11.1138.45 Marked White 88.80 −2.39 8.38 174-115E 174-115E 49.80 2.78 6.91−38.99 5.17 −1.47 39.36 Marked White 86.34 −1.17 4.38 174-115C 174-115C53.00 2.06 2.68 −33.34 3.22 −1.71 33.54 Marked White 95.46 −0.99 2.23R960 R960 91.38 −0.89 2.47 −4.07 0.10 0.24 4.08 Marked

[0086] The results listed in Table 1 illustrate the high contrastbetween the marked and unmarked epoxy coating samples incorporating thebismuth-containing compositions, in comparison with a coating samplecontaining a standard TiO₂ pigment designated R960 in Table 1. The ΔLvalues from the samples comprising the present bismuth-containingcompositions are over 20, and in many cases over 30.

[0087] Table 2 lists the color values of each plastic sample before andafter laser marking. TABLE 2 Plastic Laser Mark Contrast Sample ID L* a*b* ΔL* Δa* Δb* ΔE* 179-115E 81.0 −0.75 11.58 Unmarked 179-115E 38.5 1.634.12 −42.46 2.38 −7.46 43.18 Marked 267-010A 84.1 1.03 9.87 Unmarked267-010A 56.9 1.88 6.62 −27.16 0.85 −3.25 27.37 Marked 267-010A′ 83.21.54 10.12 Unmarked 267-010A′ 59.3 2.00 6.81 −23.88 0.46 −3.31 24.12Marked 267-011A 86.7 −0.18 10.78 Unmarked 267-011A 52.5 2.01 6.05 −34.252.19 −4.73 34.65 Marked 267-012B 81.5 −3.71 20.64 Unmarked 267-012B 36.92.28 4.48 −44.62 5.99 −16.16 47.83 Marked 267-013A 86.1 −5.16 23.18Unmarked 267-013A 48.2 1.11 6.80 −37.89 6.27 −16.38 41.75 Marked267-016B 75.9 4.11 45.11 Unmarked 267-016B 42.8 1.34 7.95 −33.14 −2.77−37.16 49.87 Marked 267-022A 83.3 −5.38 23.76 Unmarked 267-022A 37.82.23 4.28 −45.51 7.61 −19.48 50.08 Marked 267-024A 82.9 −4.05 35.10Unmarked 267-024A 35.2 2.04 3.46 −47.68 6.09 −31.64 57.54 Marked267-038A 86.0 −2.08 15.55 Unmarked 267-038A 44.0 1.29 2.89 −42.04 3.37−12.66 44.03 Marked 267-047A 85.8 −3.57 14.99 Unmarked 267-047A 49.60.96 6.40 −36.19 4.53 −8.59 37.47 Marked 267-049A 84.6 −3.55 37.92Unmarked 267-049A 50.2 −0.21 10.58 −34.37 3.33 −27.34 44.04 Marked267059A 87.1 −6.67 27.10 Unmarked 267-059A 41.8 1.48 4.40 −45.29 8.15−22.70 51.31 Marked

[0088] The results listed in Table 2 illustrate the high contrastbetween the marked and unmarked plastic samples incorporating thebismuth-containing compositions. The ΔL values are greater than 20, andmost are over 30 or 40.

[0089] In accordance with an embodiment of the present invention, anadvantageous property of the compounds is good infrared reflectance.These infrared reflective properties were tested versus various othercommercial pigments, and the measurements have shown that the presentcompositions exhibit low heat buildup properties. Thus, for reduced heatbuild-up in applications such as architectural, military, marine vesselpaint, automotive paint and vinyl siding applications, the presentbismuth-containing compounds have a very wide use potential.

[0090] In order to demonstrate the visible and IR reflectancecharacteristics of the present bismuth-containing materials, some of theepoxy coating samples listed in Table 1 were tested for reflectance atwavelengths of from 300 to 2,500 nm. Graphs showing reflectance versuswavelength data for some of the epoxy coating samples are provided inFIGS. 2-11. Comparison curves for similar epoxy samples containingconventional TiO₂, 10401 (NiSbTi), and 10408 (CrSbTi) pigments areprovided in FIGS. 12-14. Favorable IR reflectance properties areachieved by the present bismuth-containing compounds.

[0091] The heat build-up results of a number of the synthesizedcompounds are listed below. TABLE 3 Heat Build-Up Results Sample Ta TmΔTlu ΔTv ΔTh Carbon Black 72.3 216.1 143.8 R960 TiO2 73.3 134.6 61.34.61 56.1 267-010-A 73.5 135.9 62.4 46.5 56.6 267-010-A 73.4 138.9 65.547.5 57.8 267-011-A 72.9 138.1 65.2 47.3 57.5 174-115-E 73.3 140.2 66.948 58.4 267-012-B 73.2 140.3 67.1 48 58.4 267-016-B 72.8 139.7 66.9 47.858.2 10401 NiSbTi 72.9 136.9 64 46.9 57.1 10408 CrSbTi 73 138.9 65.947.6 57.8

[0092] Table 3 illustrates low heat build up properties for the darkercolor shades, which is comparable to the lighter TiO₂. Comparable IRreflectance performance is also shown in Table 3 for the presentbismuth-containing compounds in comparison with standard 10401 and 10408pigments used in the vinyl siding industry, which are known to be goodfor IR reflecting and heat build-up.

[0093] Whereas particular embodiments of this invention have beendescribed above for purposes of illustration, it will be evident tothose skilled in the art that numerous variations of the details of thepresent invention may be made without departing from the invention asdefined in the appended claims.

What is claimed is:
 1. A pigment of the formula Bi_(x)M_(y)O_(z), whereM is at least one metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr,Si, Y, Nb, La, Ta, Pr, Ca, Mg, Mo, W, Sb, Cr, Ba and Ce, x is from about0.3 to about 70, y is from about 0.05 to about 8, z is from about 1 toabout 100, and the ratio of x to y is greater than
 2. 2. The pigment ofclaim 1, wherein the ratio of x to y is greater than
 5. 3. The pigmentof claim 1, wherein the ratio of x to y is greater than
 10. 4. Thepigment of claim 1, wherein the ratio of x to y is greater than
 20. 5.The pigment of claim 1, wherein M comprises Zn, Si, Zr, Al or Sn.
 6. Thepigment of claim 1, wherein the pigment is markable by a laser.
 7. Alaser markable compound comprising an oxide of bismuth and at least oneadditional metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y,Nb, La, Ta, Pr, Ca and Mg.
 8. The laser markable compound of claim 7,wherein the compound is of the formula Bi_(x)M_(y)O_(z), where M is atleast one metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y,Nb, La, Ta, Pr, Ca, Mg, Mo, W, Sb, Cr, Ba and Ce, x is from about 0.3 toabout 70, y is from about 0.05 to about 8, and z is from about 1 to 100.9. The laser markable compound of claim 8, wherein the ratio of x to yis greater than
 2. 10. The laser markable compound of claim 8, whereinthe ratio of x to y is greater than
 5. 11. The laser markable compoundof claim 8, wherein the ratio of x to y is greater than
 10. 12. Thelaser markable compound of claim 8, wherein M comprises Zn, Si, Zr, Alor Sn.
 13. A laser markable substrate comprising: a substrate material;and a bismuth-containing compound dispersed in the substrate material.14. The laser markable substrate of claim 13, wherein thebismuth-containing compound comprises an oxide of bismuth and at leastone additional metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr,Si, Y, Nb, La, Ta, Pr, Ca and Mg.
 15. The laser markable substrate ofclaim 13, wherein the bismuth-containing compound comprises the formulaBi_(x)M_(y)O_(z), where M is at least one metal selected from Zn, Ti,Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr, Ca and Mg, x is fromabout 0.3 to about 70, y is from about 0.05 to about 8, and z is fromabout 1 to
 100. 16. The laser markable substrate of claim 15, whereinthe ratio of x to y is greater than
 2. 17. The laser markable substrateof claim 15, wherein the ratio of x to y is greater than
 5. 18. Thelaser markable substrate of claim 15, wherein the ratio of x to y isgreater than
 10. 19. The laser markable substrate of claim 15, wherein Mcomprises Zn, Si, Zr, Al or Sn.
 20. The laser markable substrate ofclaim 13, wherein the bismuth-containing compound comprises from about0.1 to about 70 weight percent of the substrate.
 21. The laser markablesubstrate of claim 13, wherein the bismuth-containing compound comprisesfrom about 2 to about 50 weight percent of the substrate.
 22. A lasermarked substrate comprising: a substrate; a bismuth-containing compounddispersed in the substrate; and a laser-marked portion of the substrateexhibiting a contrasting mark compared with a non-laser marked portionof the substrate.
 23. The laser marked substrate of claim 22, whereinthe laser-marked portion and the non-laser marked portion of thesubstrate have a different lightness value ΔL of greater than about 20.24. The laser marked substrate of claim 22, wherein the laser-markedportion and the non-laser marked portion of the substrate have adifferent lightness value ΔL of greater than about
 25. 25. The lasermarked substrate of claim 22, wherein the laser-marked portion and thenon-laser marked portion of the substrate have a different lightnessvalue ΔL of greater than about
 30. 26. The laser marked substrate ofclaim 22, wherein the laser-marked portion and the non-laser markedportion of the substrate have a different lightness value ΔL of greaterthan about
 35. 27. The laser marked substrate of claim 22, wherein thelaser-marked portion and the non-laser marked portion of the substratehave a different lightness value ΔL of greater than about
 40. 28. Thelaser marked substrate of claim 22, wherein the bismuth-containingcompound comprises the formula Bi_(x)M_(y)O_(z), where M is selectedfrom Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr, Ca, Mg,Mo, W, Sb, Cr, Ba and Ce, x is from about 0.3 to about 70, y is fromabout 0.05 to about 8, and z is from about 1 to
 100. 29. The lasermarked substrate of claim 28, wherein the ratio of x to y is greaterthan
 2. 30. The laser marked substrate of claim 28, wherein the ratio ofx to y is greater than
 5. 31. The laser marked substrate of claim 28,wherein the ratio of x to y is greater than
 10. 32. The laser markedsubstrate of claim 28, wherein M comprises Zn, Si, Zr, Al or Sn.
 33. Amethod of making a laser markable compound comprising: mixing bismuthoxide or precursors thereof with at least one additional metal oxide orprecursors thereof; and heating the mixture.
 34. The method of claim 33,wherein the compound comprises the formula Bi_(x)M_(y)O_(z), where M isat least one metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr, Si,Y, Nb, La, Ta, Pr, Ca, Mg, Mo, W, Sb, Cr, Ba and Ce, x is from about 0.3to about 70, y is from about 0.05 to about 8, and z is from about 1 to100.
 35. A method of making a laser markable substrate comprisingdispersing a bismuth-containing compound in a substrate material,wherein the bismuth-containing compound comprises an oxide of bismuthand at least one additional metal selected from Zn, Ti, Fe, Cu, Al, Zr,P, Sn, Sr, Si, Y, Nb, La, Ta, Pr, Ca and Mg.
 36. A method of lasermarking an article comprising: providing a substrate including abismuth-containing compound; and irradiating at least a portion of thesubstrate with a laser to form a marking thereon.
 37. The method ofclaim 36, wherein the bismuth-containing compound comprises an oxide ofbismuth and at least one additional metal selected from Zn, Ti, Fe, Cu,Al, Zr, P, Sn, Sr, Si, Y, Nb, La, Ta, Pr, Ca and Mg.
 38. The method ofclaim 36, wherein the compound is of the formula Bi_(x)M_(y)O_(z), whereM is at least one metal selected from Zn, Ti, Fe, Cu, Al, Zr, P, Sn, Sr,Si, Y, Nb, La, Ta, Pr, Ca, Mg, Mo, W, Sb, Cr, Ba and Ce, x is from about0.3 to about 70, y is from about 0.05 to about 8, and z is from about 1to 100.